1. Field of the Invention
The present invention relates to a method for transmitting/receiving audio/video contents in wireless access networks and an apparatus thereof, which are capable of enhancing the data rate of high SINR users and maintaining the data rate of low SINR users by combining spatial multiplexing and layered source coding together.
2. Description of Prior Art
In wireless access networks, multimedia broadcast and multicast services have been paid lots of attention. Users are able to watch online video or audio programs from the networks and it also brings increasing revenues for telecom operators including fixed and mobile operators. Limited by the wireless propagation environments, at the receiver different users usually have different signal interference noise ratios (SINR) and different achievable data rates. To transfer the same volume of data to users with different SINR in a cell, the traditional methods were proposed by expanding the operating channel bandwidth, but it will result in low resource utilization. To guarantee each user to enjoy the program fairly, the lowest achievable data rate has to be adopted to deliver broadcasting and multicasting services to all users.
The best existing solution to this problem is the layered modulation combined with source coding. By utilizing source coding techniques, the original video or audio information is encoded into two different quality-level streams: basic stream and advanced stream. In the modulation phase, each modulation constellation of the basic stream is the center of the constellation in each quadrant of the advanced one. Coded bits of basic stream and advanced stream are modulated on the constellation with larger Euclidean and smaller Euclidean distance, respectively. If the user terminal has high enough SINR, it will demodulate the coded bits carried by constellation with both larger Euclidean and smaller Euclidean distance; if the user has low SINR, the coded bits carried by constellation with larger Euclidean distance can be demodulated.
However this method has the disadvantages as follows. It requires large modification effort at PHY and MAC layer in the system, and cannot be directly applied to existing systems. The demodulation at receiver is much more complicated than traditional demodulation.